Two-pump supply for hydraulic circuits having different flow requirements



NOV. 7, 1967 J J BERTA ET AL 3,350,986

TWO-PUMP SUPPLY FOR HYDRAULIC CIRCUITS 'HAVING DIFFERENT FLOW REQUIREMENTS Filed March 17, 1966 RE SER VOl R INVENTORS JAMES J. BERTA JAMES E. Sea-451m" United States Patent M TWO-PUMP SUPPLY FOR HYDRAULIC CIRCUITS HAVING DIFFERENT FLOW REQUIREMENTS James J. Berta, Braidwood, and James E. Scheidt, Joliet,

Ill., assignors to Caterpillar Tractor Co., Peoria, 111., a

corporation of California Filed Mar. 17, 1966, Ser. No. 535,096 Claims. (Cl. 91-414) The present invention relates to an improved hydraulic control circuit for operating a plurality of hydraulic motors of different capacities, and more particularly to a twopump control circuit in which the volume from one pump is selectively directed to a first hydraulic motor circuit, and is then combined under all operating conditions with the volume of the second pump, the combined volume accordingly being available for direction to one or more subsequent hydraulic motor circuits. The invention further provides each subsequent hydraulic motor circuit with substantially the full combined volume from both pumps irrespective of the operating conditions of the preceding subsequent circuits.

In hydraulic control circuits having ditferent flow requirements wherein only a single pump is used, it is common practice to use a pump having a flow capacity equal to the requirements of the circuit having the largest flow capacity. A flow control valve is then provided in the hydraulic circuit having the smaller flow capacity or requirement, to reduce the volume of oil supplied thereto. Since flow control valves generally operate in response to a pressure differential across a restriction, the pump is required to work against the pressure required to operate the flow control valve, in addition to the pressure required to accomplish the desired work function. Since the pump volume in excess of that required for the low flow capacity circuit is bypassed back to the reservoir through the flow control valve, this results in inefliciency due to use of available horsepower in excess of that required to do the actual work being performed and generation of excess heat in the circuit.

Circuits employing two pumps are available, wherein one of the pumps is used to supply the low flow capacity circuit and when the valve of such circuit is in a neutral position, the volume of that pump is combined with that of a second pump for supply to the circuit having the larger flow capacity. These circuits have been generally unsatisfactory since when the low volume circuit is operative, the volume of the first pump is not available to supplement the volume of the second pump for supply to the second circuit. This results in variations in the volume available to the second circuit, and particularly results in an inadequate flow of oil to the second circuit at such time as the first circuit is operative, whereby the speed of operation of the second circuit is reduced. Accordingly, it is desirable that a circuit be provided wherein a constant volume of fluid is supplied to the hydraulic motor circuit having low flow requirements, and that fluid from that circuit be available at all times to supplement continuously the volume of the second pump which supplies a second circuit having higher flow requirements.

Accordingly, it is an object of the invention to provide a two-pump hydraulic control circuit wherein the volume of one pump is directed to a first hydraulic motor circuit for selective operation thereof, but wherein such volume is furthermore available to continuously supplement the volume of the second pump, irrespective of the operating condition of the first circuit.

It is another object of the invention to provide a twopump control circuit wherein the volumes of both the pumps are substantially combined at all times for subsequent use in further hydraulic motor circuits.

3,350,986 Patented Nov. 7, 1967 It is a further object of the invention to provide a twopump hydraulic control circuit wherein each of a plurality of hydraulic motor circuits disposed subsequent to a first hydraulic motor circuit, is supplied with essentially the full combined volume of both the pumps.

It is yet another object of the invention to provide a double pump source hydraulic control circuit wherein a plurality of hydraulic motors is each supplied with essentially the full output volume from one of the double pump sources regardless of the operating conditions of the remaining hydraulic motors, and wherein a subsequent plurality of hydraulic motors is each supplied with essentially the full combined output of the double pump source regardless of the operating conditions of the remaining hydraulic motors of either plurality of hydraulic motors.

Further objects and advantages will be apparent from the following description and drawing, wherein the single figure is a diagrammatic presentation of the hydraulic control circuit and including a sectional view of the valve means employed, in accordance with the invention, as utilized in a bulldozer.

Briefly, the invention contemplates the use of two pumps, wherein only the volume of the smaller pump is directed to a blade tilt hydraulic motor circuit for actuation of the blade tilt mechanism, thereby precluding the need for a flow control valve such as previously mentioned, that has been used in the past with single pump control systems. The invention further employs a tilt control valve connected in the flow path between the small pump and the blade tilt circuit, which is designed such that when the tilt valve spool is in a neutral position the fluid from the small pump is combined with the fluid from the small pump is combined with the fluid from the large pump, and is thereafter directed to a second or lift valve and thence to a blade lift hydraulic motor circuit for control of the blade lift mechanism. The tilt valve is also designed such that when its spool is in a position directing fluid pressure from the small pump to either end of the tilt hydraulic motor, the fluid displaced from the opposite end thereof is combined with the volume of the large pump for supply to the second or lift valve.

Thus the large pump volume is supplemented at all times with the tilt circuit volume to provide an optimum volume for effecting the desired speed of actaution for the blade lift mechanism, while simultaneously reducing the capacity requirements for the large pump and minimizing horsepower losses and heat generation in the circuit.

Further in accordance with the invention the bulldozer ripper mechanism is actuated via a ripper hydraulic motor circuit, which includes a ripper valve connected in series with the lift valve, wherein the combined volumes of the two pumps are subsequently available for actuation of the ripper mechanism. Thus a relatively constant and larger volume of fluid is always available to the lift valve as well as the ripper valve for control of the bulldozer blade lift and the ripper mechanisms.

Referring now to the figure, there is shown a two-pump hydraulic control circuit of the present invention, comprising a pair of hydraulic pumps 10 and 12 of generally small and large flow capacity, respectively, for supplying fluid under preselected pressure to a pair of immediate hydraulic motor circuits indicated generally by numerals 14 and 16 and termed blade tilt and blade lift circuits, respectively.

The pumps 10 and 12 are adapted to draw fluid from a hydraulic reservoir 18. Small pump 10 supplies a selected volume of fluid under preselected pressure through a discharge conduit 20 to an inlet port of a tilt control valve 22 associated with the tilt circuit 14. The large pump 12 supplies a selected volume of fluid under preselected pressure through a discharge conduit 24 to an -inlet port of a lift control valve 26 associated with the lift circuit 16.

The tilt valve 22 is provided with an outlet passage 28 connected via a conduit 38 to the discharge conduit 24, and also is provided with a fluid directing valve spool 32. A check valve 34 is connected between the discharge conduit 20 and a second inlet port of valve 22 via a conduit 36. A double-acting tilt hydraulic motor 38, having a piston 40, is connected to the tilt control valve 22 at its head and rod end via conduits 42 and 44, respectively.

The lift valve 26 is designed to operate in a manner similar to the operation of tilt valve 22, and is provided with a valve spool 46, outlet conduits 48, and an internally disposed check valve 50 connected via conduit 52 from the junction of the discharge conduit 24 and conduit 30, to a second inlet port of lift valve 26.

A double-acting hydraulic motor 54 of large capacity and including a double piston configuration 5-6, is connected to the lift control valve 26 at the head and rod ends thereof via conduits 58 and 60, respectively.

The outlet conduits 48 of lift valve 26 are in turn in common communication with an inlet port of a ripper control valve 62 via a conduit 64. A check valve 66 is connected between conduit 64 and a second inlet port of the ripper valve 62. A valve spool 68 is provided in control valve 62, which is similar in design to lift control valve 26, and a double-acting ripper hydraulic motor 70 having a piston 72 is disposed in communication at its head and rod end to control valve 62 via conduits 74 and 76, respectively, the combination defining thus a ripper hydraulic motor circuit 78 similar to the blade lift circuit 16.

The ripper control valve 62 is provided with outlet conduits 80, which are in common commnnication with the reservoir 18 via a single return conduit 82. Note that the only path for fluid return to the reservoir is from the ripper valve 62 via conduits 80 and 82. Thus, in accordance with the invention, the individual and then combined fluid volume from both pumps and 12 passes through all the valves 22, 26 and 62, prior to being returned to the reservoir 18.

Relief valves 84 and 86 are provided between the discharge conduits 24 and 20, respectively, and reservoir 18, to bypass fluid back to the reservoir 18 in the event the pressures delivered by the pumps exceed a preselected maximum safe value.

In operation, tilt circuit 14 requires a relatively low volume of fluid to achieve the desired speed of actuation of the hydraulic motor 38, whereas the larger capacity lift circuit 16 requires a relatively higher volume of fluid to achieve the desired speed of actuation of the double piston hydraulic motor 54.

To this end, when the spool 32 of the tilt control valve 22 is in the neutral position, as shown in the figure, the fluid discharge of the pump 10 is directed through the valve 22 via the outlet passage 28, and thence through conduit 30 to combine with the fluid in discharge conduit 24 and is then directed to the lift valve 26 via the conduit 52.

Thus it may be seen that when the spool 32 is in the neutral position, the combined volumes of pumps 18 and 12 are available to the lift control valve 26. Upon movement of the spool 46 of the lift control valve 26 to either of its two operative positions, the combined volume of both pumps 10 and 12 is directed to the hydraulic motor 54 which is accordingly actuated at the desired speed commensurate with the combined volumes.

In accordance with the invention, fluid is available via the conduit 30 at all times to continuously supplement the volume of pump 12 under all operating conditions, thereby maintaining a constant speed of actuation of the motor 54. To this end, control valve 22 is designated such that when the spool 32 thereof is moved to either of its two operative positions to actuate the hydraulic motor 38 in the respective direction, the fluid displaced from the opposite end of the motor by movement of the piston 40 is directed from the motor out through either of passages 42 or 44, across spool 32 and from thence through the passage 28 and conduit 30 to supplement the volume of pump 12.

For example, when spool 32 is moved to the right, communication between conduit 20 and passage 28 is blocked by the lands thereon. Because of such blockage, pressure builds up in conduit 20 and the fluid discharge of pump 10 is directed through the check valve 34, the conduit 36, across the spool 32 and through the conduit 42 to the head end of the motor 38. Since this position of spool 32 also provides communication between the conduit 44 and passage 28, the fluid pressure in the head end of the motor 38 moves piston 40 to the right, and fluid displaced from the rod end thereof is directed through conduit 44, passage 28, and conduit 30, to where it is combined with the pump 12 volume for supply via conduit 52 to the lift valve 26.

The volume of fluid displaced from the rod end of motor 38, under the above-described conditions, will be slightly less than the pump volume due to the displacement differential between the opposite ends of the cylinder resulting from the area occupied by the piston rod. The percentage of variation in the total volume supplied to valve 26 will be relatively small and, therefore, the slight loss in total volume available to motor 54 will be inconsequential.

When spool 32 of the valve 22 is moved to the left, the direct passage across spool 32 from conduits 20 to 28 is once again blocked and the volume of pump 10 is directed through check valve 34 and passage 36 across spool 32 and from thence through conduit 44 to the rod end of motor 38. The volume of fluid displaced from the head end thereof will be slightly greater than the volume received from pump 10. This displaced fluid, which is communicated through conduit 42, passage 28, and conduit 30 to the discharge conduit 24 of pump 12 where it combines with the output fluid of pump 12. This results in only a slight increase in the total volume of fluid available for actuation of the motor 54.

The control valve 26 operates in a manner similar to that of control valve 22. That is, when spool 46 thereof is moved to the right, the combined volumes of fluid from the pumps 10 and 12, is directed through the check valve 50 and conduit 58, to the head end of the hydraulic motor 54.

Movement of the double piston configuration 56 to the right causes a displacement of fluid from the rod end of the motor 54 slightly smaller than the combined pump volume, which is directed through conduit 60, across valve spool 46, into one of outlet conduits 48 and from thence to ripper valve 62 via conduit 64.

When the spool 46 of valve 26 is moved to the left, the pressure fluid is directed through conduit 60 to the rod end of motor 54, and the slightly greater displaced volume passes through conduit 58 across spool 46 and on to the ripper valve 62.

When the spool 46 of valve 26 is in neutral, the combined volume of pumps 10 and 12 passes directly through the valve 26, to one of outlet conduits 48, to conduit 64 and thence to the valve 62.

Since valve 26 is identical to valve 22 to the extent that fluid leaving the valve, whether it be directly from conduit 24 or returning from motor 54, is available to the conduit 64, it is possible to connect one or more circuits such as the ripper circuit 78 in series with the lift circuit 16 for actuation of additional hydraulic circuits and associated mechanisms.

Accordingly, by utilizing the ripper valve 62, which is identical with the lift valve 26, the operation of the ripper circuit 78 will be analogous to that of the lift circuit 16. That is, the volume of fluid supplied through conduit 64 to the valve 62 can be directed to either side of the ripper hydraulic motor 70, whereupon the displaced volume of fluid at the opposite end of the motor 70 will be directed out conduits 80, to the single return conduit 82 and back to the reservoir 18.

If the spool 68 of the valve 62 is in neutral, the combined volume of fluid will pass directly through the valve 62 to return to the reservoir 18.

Thus it can be seen that a relatively constant volume of fluid commensurate with that required to provide the desired speed of actuation of motor 38 is supplied to the valve 22 without necessitating that the pump work against an increased back pressure resulting from the use of flow control valves, such as utilized in some prior art control circuits. The circuit of the invention, therefore, makes the most eflicient use of the available horsepower and keeps heat generation in the hydraulic circuit to a minimum value. Furthermore, unlike prior art circuits, a substantially constant volume of fluid is available via conduit to supplement the discharge of the pump 12 and thus supply a relatively large constant volume of fluid, under all circuit operating conditions, to one or a series of subsequent circuits such as circuits 16 and 78.

Although only a single circuit is shown in the hydraulic system as being supplied by pump 10, it is to be understood that several circuits corresponding in flow requirements to tilt circuit 14 could be supplied by the pump 18 prior to combining the volume therefrom with the volume of pump 12. Such is accomplished by merely inserting additional valves such as valve 22, into the conduits 20 or 30, for control of associated circuits which are in turn similar to circuit 14. Additionally, the high capacity motors could be placed in the first part of the system, e.g., as circuit 14, and the low capacity motors could be defined as circuits 16 or 78.

Thus, although the invention has been exemplified herein as but a single embodiment, various modifications can be made within the spirit of the invention, and it is not intended to limit the scope thereof except as defined in the following claims.

We claim:

1. A hydraulic control circuit for operating a plurality of hydraulic motors of different capacities, including a first relatively low capacity hydraulic pump means for supplying at least one relatively low capacity motor, a second relatively high capacity pump means for supplying at least one subsequent relatively high capacity motor, and a fluid reservoir in communication with the pump means, the improvement comprising; valve means intercommunicating the pump means and the motors to combine substantially the full volume of the first pump means with the second pump means volume being directed to a subsequent motor regardless of the operating condition of a first motor operated by the output volume of said first pump, said valve means further adapted to direct said resulting combined volume to the subsequent motor to selectively actuate same prior to returning the combined volume to the fluid reservoir.

2. A hydraulic control circuit for operating first and second hydraulic motors of low and high capacity, respectively, comprising; a first and second hydraulic pump of relatively low and high pumping capacity, respectively, said pumps having respective outlets, and inlets in communication with a fluid reservoir; first valve means connected between said first pump outlet and the first hydraulic motor to selectively direct the first pump fluid volume to the first motor; second valve means connected between said second pump outlet and the second hydraulic motor to selectively direct the second pump fluid volume to the second motor; said first valve means being adapted to combine substantially the full fluid volume from said first pump with the fluid volume from the second pump being directed to the second valve means regardless of the operating condition of the first motor; said second valve means being adapted to selectively direct the resulting combined fluid volumes to the second motor for actuation 6. thereof prior to passing substantially the combined fluid volumes therefrom.

3. The hydraulic control circuit of claim 2 wherein the first valve means has an internal chamber and a fluid directing spool disposed in axially translatable relation therein, wherein placement of the spool in a neutral position allows the first pump volume to pass directly therethrough to be combined with the fluid volume of the second pump, and wherein translation of the spood to an operative position selectively directs the first pump volume to the first motor to actuate same, and thence combines the volume displaced by the actuated first motor with the fluid volume of the second pump.

4. The hydraulic control circuit of claim 2 wherein the second valve means has an internal chamber and a fluid directing spool disposed in axially translatable relation therein, wherein placement of the spool in a neutral position allows said resulting combined fluid volumes to pass directly therethrough, and wherein translation of the spool to an operative position selectively directs the combined fluid volumes to the second motor to actuate same, whereupon the resulting volume displaced by the actuated second motor is directed through the second valve means to pass therefrom.

5. The hydraulic control circuit of claim 2 wherein the first and second motors are of low and high capacity, respectively, have reciprocating pistons and can be selectively actuated from either the head or rod end thereof, the circuit further comprising: first and second valve means having internal chambers and first and second fluid directing spools respectively disposed to axially translated between a neutral and two operative positions within the chambers, wherein placement of the first spool in the neutral position directs the first pump volume directly therethr-ough to communicate same with the second pump outlet to combine with the volume thereof, wherein translation of the first spool to either of the operative positions selectively directs the first pump volume to an end of the first motor to actuate same, the volume displaced from the opposite end of said actuated first motor being in communication with the second pump outlet to combine with the volume thereof; wherein placement of the second spool of the second valve means in the neutral position directs the combined volumes received thereby directly through the second valve means, wherein translation of said second spool to either of the two operative positions selectively directs the combined volumes to one end of said second motor to selectively actuate same, the volume displaced from the other end of said second motor being directed therefrom to pass through the second valve means.

6. The hydraulic control circuit of claim 5 further comprising, third valve means in communication with the second valve means and adapted to receive the combined volumes from said second valve means, and a third hydraulic motor having a relatively high capacity coupled to said third valve means, wherein said third valve means is adapted to selectively direct said received volumes to the third motor for actuation thereof, whereupon substantially the full combined volume is returned to the third valve means and directed therefrom to said reservoir.

7. The hydraulic control circuit of claim 6 further comprising: first fluid conduit means extending from said first pump outlet to an inlet port in said first valve means, second and third fluid conduit means coupled between said first valve means and respective ends of said first motor, fourth fluid conduit means extending from said second pump outlet to an inlet port in said second valve means, fifth fluid conduit means extending between an outlet port in said first valve means and said fourth fluid conduit means, sixth and seventh fluid conduit means coupled between said second valve means and respective ends of said second motor, eighth fluid conduit means extending from an outlet port in said second valve means to an inlet port of said third valve means, ninth and tenth fluid conduit means coupled between said third valve means and respective ends of said third motor, eleventh fluid conduit means extending from an outlet port in said third valve means to said reservoir, and twelfth fluid conduit means coupled between said reservoir and said pumps.

8. The hydraulic control circuit of claim 7 wherein substantially the full volume from said first pump is combined with the volume of said second pump via said first valve means and said fifth fluid conduit means regardless of the operating condition of said first motor, said combined volumes are directed to said third valve means via said fourth and eighth fluid conduit means and said second valve means regardless of the operating conditions of said second motor, and the resulting combined volumes are directed to the reservoir via said third valve means and said eleventh fluid conduit means regardless of the operating condition of said third motor.

9. The hydraulic control circuit of claim 8 wherein, said first valve means when in an operative position selectively directs said first pump volume and receives the displaced volume to and from said first motor via the second and third fluid conduit means and thereafter combines the first motor displaced volume with the second pump output via said fifth fluid conduit means, said second valve means when in an operative position selectively directs said combined volumes and receives the resulting displaced volume to and from said second motor via the sixth and seventh fluid conduit means and thereafter directs the resulting displaced volume therefrom, and said third valve means when in an operative position actuates the third motor in a similar manner via the ninth and tenth fluid conduit means whereupon the third motor displaced volume is directed via the third valve means and said eleventh fluid conduit means to said reservoir.

10. The hydraulic control circuit of claim 9 wherein said first valve means when in a neutral position combines the first pump volume with the second pump volume via the fifth fluid conduit means, and said second and third valve means when in the neutral position successively passes the combined volumes to said reservoir via the eighth and eleventh fluid conduit means.

References Cited UNITED STATES PATENTS 2,052,182 8/1936 Le Bleu 60--52 X 3,032,994 5/1962 Lindell 60--52 3,146,593 9/1964 Stacey 60-52 3,156,098 11/1964 La R011 6097 EDGAR W. GEOGHEGAN, Primary Examiner. 

1. A HYDRAULIC CONTROL CIRCUIT FOR OPERATING A PLURALITY OF HYDRAULIC MOTORS OF DIFFERENT CAPACITIES, INCLUDING A FIRST RELATIVELY LOW CAPACITY HYDRAULIC PUMP MEANS FOR SUPPLYING AT LEAST ONE RELATIVELY LOW CAPACITY MOTOR, A SECOND RELATIVELY HIGH CAPACITY PUMP MEANS FOR SUPPLYING AT LEAST ONE SUBSEQUENT RELATIVELY HIGH CAPACITY MOTOR, AND A FLUID RESERVOIR IN COMMUNICATION WITH THE PUMP MEANS, THE IMPROVEMENT COMPRISING; VALVE MEANS INTERCOMMUNICATING THE PUMP MEANS AND THE MOTORS TO COMBINE SUSBTANTIALLY THE FULL VOLUME OF THE FIRST PUMP MEANS WITH THE SECOND PUMP MEANS VOLUME BEING DIRECTED TO A SUBSEQUENT MOTOR REGARDLESS OF THE OPERATING CONDITION OF A FIRST MOTOR OPERATED BY THE OUTPUT VOLUME OF SAID FIRST PUMP, SAID VALVE MEANS FURTHER ADAPTED TO DIRECT SAID RESULTING COMBINED VOLUME TO THE SUBSEQUENT MOTOR TO SELECTIVELY ACTUATE SAME PRIOR TO RETURNING THE COMBINED VOLUME TO THE FLUID RESERVOIR. 